In recent years, a small-sized imaging module has been mainly used for camera-equipped mobile device such as a mobile phone or mobile terminal (PDA). In such an imaging module, an imaging sensor having a plurality of light receiving elements for performing photoelectric conversion of incident light from an object is modularized (integrated) with a lens for focusing the incident light on the imaging sensor.
The small-sized imaging module includes a sensor chip (solid-state imaging chip) arranged on a substrate that is mainly made of ceramic, glass-impregnated epoxy resin, or the like. The imaging sensor having the plurality of light receiving elements arranged in a two-dimensional array is disposed on the center part of the sensor chip.
The small-sized imaging module also includes an actuator. The actuator vertically moves a holder, in which a lens for focusing the incident light on the imaging sensor is fixed, in the small-sized imaging module. Here, a camera module 100a is illustrated in FIG. 8 as an example of the small-sized imaging module.
The camera module 100a has a sensor chip 110 attached on a substrate 109 with an adhesive (not illustrated). A plurality of pads (not illustrated) are provided on an outer peripheral portion of the sensor chip 110 and the pads are wire-bonded with respective terminals (not illustrated) on the substrate 109 with wires 111 for electrical connection.
The camera module 100a further includes an actuator 101. The actuator 101 includes a holder 104, a coil 105 wounded on an outer periphery of the holder 104, a yoke 107, a magnet 106, and a base 108 fixed to the substrate 109. The yoke 107 is a metal member and electrically shields the camera module 100a, which is provided on an outer periphery of the coil 105, from its outside. The magnet 106 is arranged on the inner side of the yoke 107 at a predetermined gap with the coil 5.
A barrel 103 is fixed with an adhesive (not illustrated) in the inside of the holder 104. Lenses 102 are surrounded by the barrel 103 and the lenses 102 are held inside the barrel 103.
When current flows through the coil 105 in the actuator 101 configured as described above, electromagnetic force is generated between the coil 105 and the magnet 106. With the electromagnetic force, the holder 104 is displaced in an optical axis direction of the lenses 102 together with the lenses 102 and the barrel 103. An amount of the displacement is controlled with an amount of the current flowing through the coil 105.
The aforementioned structure of the actuator 101 is a general VCM (Voice Coil Motor) structure.
In manufacturing of the camera module 100a, when the base 108 is fixed to the substrate 109 with an adhesive 114, the actuator 101 is fixed to the substrate 109. At this time, an IR cut filter 112 is inserted and fixed between the sensor chip 110 and the lenses 102. By this IR cut filter 112, entrance of infrared light to the sensor chip 110 is eliminated.
In the process described above, the actuator 101 needs to be fixed to the substrate 109 so that an image is formed accurately on an imaging surface of the sensor chip 110. When a relative positional shift is caused between the lenses 102 and the imaging surface of the sensor chip 110 or the optical axis is tilted, however, there is a problem of causing shading or partial blur resulting from a positional shift of a light flux, which comes through the lenses 102, in the imaging surface.
In particular, due to usage of the adhesive 114 for fixing the actuator 101 to the substrate 109, the base 108 may move while the adhesive 114 is being cured (for example, high temperature storage) in some cases, so that a relative positional shift, a tilt, or the like is easily caused.
Further, in the case of the VCM, there is also a problem of easily causing partial blur due to occurrence of a moving tilt or the like because the holder 104 is fixed to the yoke 107 and the base 108 with relatively weak force by a spring (not illustrated) or the like.
In order to solve the aforementioned problems, PTL 1 and PTL 2 describe a camera module and a solid-state imaging device, respectively, in which a lens is further provided over an imaging sensor and positioning of the imaging sensor and the lens is performed accurately with a positioning mechanism provided around the lens.
In detail, PTL 2 describes the solid-state imaging device which includes a barrel for holding a first lens, a driving mechanism for adjusting a position of the first lens in an optical axis direction of the first lens, and a structure which abuts the barrel so that the first lens faces a solid-state imaging sensor, in which the first lens is held by the barrel, and a second lens is provided in an inner peripheral portion of the structure. In this solid-state imaging device, the barrel abuts against a tilt portion provided in the structure and is thereby fixed thereto, so that it is possible to determine a positional relation between the first lens and the second lens and further a positional relation between the position of the first lens and the center of the solid-state imaging sensor.
The camera module described in PTL 1 will be described with reference to FIG. 9. Note that, for convenience of the description, the same reference signs will be assigned to the members having the same functions as the members described in FIG. 8, and the description thereof will be omitted.
As illustrated in FIG. 9, in a camera module 100b, a fixed lens 117 is provided over the substrate 109 and is arranged between the lenses 102 and the sensor chip 110 (imaging sensor). A positioning member 116 abutting the actuator 101 is formed in an outer peripheral portion of the fixed lens 117. A cover 115 formed in a shape covering almost lower surfaces of the holder 104, the coil 105, and the magnet 106 is also included.
The lenses described in PTL 1 and PTL 2 also function to correct distortion aberration or incident light.